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  #1  
Old 04-06-2008, 12:30 PM
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lordxale lordxale is offline
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pioneer s-hf21-lr crossover mod?

I have a pair of Pioneer S-HF21-LR speakers that I got a couple years back on black friday for $10, and since I've had them I've never been terribly impressed and now I have the urge to tinker with them

For those unacquainted with them, they're the lowest end model in Pioneers current retail-market speakers. Single 5 1/4" woofer with a quote "1-inch (2.5cm) High-Efficiency Semi-Dome Tweeter". Whatever, they're too inefficient (80dB/1w/1m) to even be used as rears with the rest of my speakers in my little home theater setup. I'd have to turn the rear level way up and for that duty my small Polk RM6000 satellites do the job better anyway. they're not great as fronts at all compared to my cheap rack stereo Pioneers or my low-budget floorstanding Kenwoods.

So, back to the speakers themselves: On the inside, they didn't really have any kind of dampening material at all except for some really thin polyfill batting stuff at the back. I've since added some (marginally more decent) polyfill stuff to all the other sides (it helped the bass not sound so boomy!), and some small rubber feet to the bottom so they don't vibrate off of my other speakers. There are also no factory sealing gaskets on either of the drivers.

The cabinet is 3/8" MDF and actually seems pretty well built. The crossover, on the other hand, is obviously pretty cheap. There are two components - a 1u5 50V capacitor wired to the tweeter and a mysterious orange-ish yellow circular device labeled T60 135 wired to the woofer. Pretty much everything I've learned I've gleaned from trolling these fine forums or otherwise googling, but so far there is a gap in my knowledge and I have no idea what this part is (I can post pictures later tonight). Some kind of low pass, I would obviously think, but what is it? My finer speakers don't have anything like this (except my big rack stereo-era Pioneers...).

Both drivers are 8 Ohm rated on the back (I know, ideally I would want to measure impedance at the desired crossover frequency), but bear with me for a moment:

I used a calculator i found with Google called "The Passive Crossover Design Calculator" written by a guy named Jeff Bagby, and, using the first-order Butterworth calculator...that's what this has to be, right? At the very least a single capacitor on the tweeter is still a first-order configuration, nevermind the woofer.

Anyway, if I'm reading the 1u5 capacitor right, that translates in to 1.5uF and therefore the tweeter is crossed at about 13250hz? Could the impedance vary that much to where 1.5uF would do the trick for the tweeter and I'm just nuts? Could two speakers really be designed as sloppily as the Presidians (I have a set of those, too )?

Since they're only a two-way and a pretty cheap design at that isn't it more likely that these suffer some kind of hole in the middle? Is it really feasible that the woofer responds up that high, or is my calculation way, way off?

Help?!? No harm in tinkering, I guess, but do I stand a chance of making them better by crossing the tweeter lower and doing something else with the woofer? Do I have a lot to learn before I should be pondering such mysteries ? ... don't answer that . Should I leave well enough alone?

Maybe I should have posted this in the "Thinking Out Loud" forum!
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  #2  
Old 04-06-2008, 08:34 PM
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lordxale lordxale is offline
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peek-ture

okay, so my cell phone takes crappy pictures but somebody in the know on the topic should still be able to distinguish what that thing is:



Again, obviously the capacitor is on the tweeter and the other thing is some kind of low pass on the woofer...but what is it?

(sorry, for some reason the AK photo uploader isn't working on my computer...probably has something to do with it being Firefox on 64-bit linux with all my add-ons and such):

...and BUMP! Geez I only have 8 views and I was already pushed to the bottom of the second page
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Old 04-06-2008, 09:41 PM
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RadShak1251 RadShak1251 is offline
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I'm assuming this is the speaker?

An 80dB SPL rating??

I gotta say I have NEVER seen a speaker, any speaker, with an efficiency rating that low. IMO that has to be a misprint (and Pioneer's own page is so screwed up I don't trust them either ).

I've actually heard that exact speaker at Circuit City and for fifty clams a pair it sounded fine to me (w/Onkyo receiver and Sony sacd player). And I didn't have to turn up the volume to a particularly high setting either.

The yellow disc-like object in the picture kind of looks like a ceramic capacitor - maybe it is functioning as some kind of hi-pass filter to prevent extremely low frequencies from reaching the small woofer?

Quote:
Is it really feasible that the woofer responds up that high,
Yep. For example, there are eight inch fullrange drivers that can make it quite smoothly up to 12kHz.
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Old 04-06-2008, 09:54 PM
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ShaneC ShaneC is offline
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pretty sure that's a ceramic cap, but that almost looks like its in paralell with the other cap...
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Old 04-06-2008, 10:16 PM
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lordxale lordxale is offline
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yeah, the pictures bad, but it's not parallel - that thing is definitely on the woofer.

And the 80dB SPL rating is even in the manual AFAIK...even my old Pioneer CS-R571 speakers are more efficient than these guys, and out of everything else I have, they're the next least efficient (btw, those are the ones with the same kind of weird component that none of my other speakers appear to have). Maybe it's just because I'm spoiled by my relatively high-efficiency SP-3500s...

Anyway, wouldn't a high pass filter for a woofer have to be a really really large value cap? These things reach down to 55hz supposedly and whether or not they actually do it I would think the cap would have to cross it that low anyway.

Even if there's not anything I can do to make them better, I still want to know what the hell that thing is!

Thanks so far, though guys...now if only Zilch would come by...
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Old 04-06-2008, 11:05 PM
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RadShak1251 RadShak1251 is offline
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Well if the manual states that, it must really be 80dB. Wow.

I'm not too surprised I guess, since I own a speaker from the series previous to this one which used basically the same woofers and enclosure design. It is a 3-way system with an 8" woofer (polypropylene cone w/rubber surround) in a ported cabinet. Its SPL rating is 89dB and while it does require a bit more twisting of my receiver's volume knob - I use them for now for my rear channel speakers - compared to my Boston CR9s (91dB rating) with their ported 8" woofer, the depth & amount of bass emanating from these bargain speakers is nearly the same as the Bostons that cost 4X more. The mids and highs, well, aren't exactly the same quality. Anyway, usually with a rating that low that means you'll get some extended bass out of a speaker vs. others of the same size.

But I would still try them out with your system - the ones I heard didn't need a high volume setting to sound the way they did. In other words, don't always trust spec charts, frequency graphs yada yada.* I'm more of an objectivist audio hobbyist myself, but know that in the end, such things only tell part of the story and you really do have to trust your ears for the final determination of what sounds good & right.


* ask others who own very accurate hi-end speakers with relatively high SPL ratings like 88-90dB about their experiences. For example, Bowers and Wilkins' 800D has a 90dB rating ($20K per pair - got to hear these with Classe monoblock amplification). That would seem like an easy speaker to drive then, right? But based on personal experience and many pro reviews, many such speakers still need powerful amps to sound their best & I don't mean a $1000 A/V receiver. Though I still haven't figured out why the printed rating for so many such speakers differs so much from real-world use.
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  #7  
Old 04-10-2008, 12:13 AM
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lordxale lordxale is offline
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Bump? can't believe there's nobody who knows what that thing is
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  #8  
Old 04-10-2008, 03:41 AM
Rolf Zetterberg Rolf Zetterberg is offline
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A ceramic cap of that size can't be larger than maybe 0,1uF-0,5uF and therefore has no great effect at audio frequencies.At RF yes,but that's of no interest here.
To me it looks like a VDR(or voltage dependent resistor or varistor)that acts like a variable resistor that changes it's resistance from very high to a very low value at a certain voltage.Almost like a zener diode.These VDRs can take enormous currents for a short time,and are therefore used as fuses in mains equipment where short spikes need to be removed.So the purpose of this component is probably to protect.
Why the designer puts it across the woofer is something of a mystery to me.It's the tweeters that needs protection.
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  #9  
Old 04-10-2008, 10:36 AM
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lordxale lordxale is offline
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Hmmm, upon further googling, yes, it does look an awful lot like a varistor, doesn't it? I tried searching for the "value" (T60 135) in google with varistor and voltage dependent resistor and still couldn't find anywhere that really confirmed it, but still ... I think the jury has probably reached its verdict.

The consensus seems to be that:

a.) We might know what it is, but we don't currently know what it does

and

b.) Things of this nature, when in such uncertainty, are almost always better left alone

Maybe I'll rip them apart again when I have something more than a rudimentary understanding of crossover networks! Thanks Rolf, and everybody else!

...but if anybody else has any ideas I'd still love to hear them!
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